Aluminium alloys

ABSTRACT

Strontium and/or calcium in a total amount of 0.01-0.5% is added to aluminium magnesium silicide extrusion alloys to reduce the formation of &#39;&#39;&#39;&#39;pick-up&#39;&#39;&#39;&#39; on extrusion at high speeds.

United States Patent 1 Morris et al.

[ Dec. 16, 1975 1 ALUMINIUM ALLOYS [75] Inventors: Larry Roy Morris,Yarker;

Frederick Barry Miners, Kingston, both of Canada [73] Assignee: AlcanResearch and Development Limited, Montreal, Canada 221 Filed: Aug. 9,1973 211 App]. No.: 386,992

[30] Foreign Application Priority Data [56] I References Cited UNITEDSTATES PATENTS 1,412,280 4/1922 Frary 75/142 2,993,784 7/1961 Huddle etal. 75/l48 3,252,841 5/1966 Foerstcr 75/l47 Primary ExaminerR. DeanAttorney, Agent, or FirmCo0per, Dunham, Clark, Griffin 81. Moran [57]ABSTRACT Strontium and/or calcium in a total amount of 0.0l0.5% 18 addedto aluminium magnesium silicide extrusion alloys to reduce the formationof pick-up" on extrusion at high speeds.

7 Claims, No Drawings ALUMINIUM ALLOYS The present invention relates toaluminium alloys containing magnesium and silicon in the general rangeof 0.3 to 1.2 weight %-Mg and 0.2 to 1.2 weight Si. An alloy of thistype containing OAS-0.9% Mg and 0.20.6% Si is the most widely used forthe production of aluminium extrusions. This alloy is widely known underthe Aluminum Association Standards as Alloy 6063. Other alloys withdifferent ranges of Mg and Si or the addition of small amounts of otherelementsare' widely used for the production of aluminium extrusions.Similar alloys are in use in other countries, although the chemicalcomposition limitsmay differ slightly from those registered with TheAluminum Association. I

The most generally used specifications for the AA 6063 class of alloyperrnits Cu, Cr, Zn, Ti and Mn to be present as impurities in amounts upto 0.1% each, while setting a maximum of 0.35% Fe and a maximum of 0.15%for other inpurities (0.05% each). In normal commercial practice,however, the total of the impurities (including Fe) is about 0.30.4%. Itis also usual for the silicon content to be in excess of that requiredto convert the whole magnesium content to Mg 'Si.

1n the as-cast condition the alloying elements and the impuritiespresent in the extrusion ingot are either in solid solution in thealuminium matrix or segregated in the form of intermetallic'phases atthe boundaries of the grains into which the alloy has solidified, or atthe boundaries of the dendrite cells within thosegrains. It has beencommon practice for some years to homogenise the structure of 6063 alloyby a heat treatment aimed at eliminating coarse particles of themagnesium silicide phase and the micro-segregation or coring ofmagnesium and silicon in the dendrite cells, since it is not possible toobtain the optimum properties or extrusion speeds in extrusions producedfrom ingots containing such segregation of magnesium and silicon. In onewidely used practice the as-cast ingots are heated for several hours ata temperature of about 550C. and cooled rapidly so as to lock a largeproportion of the magnesium silicide in solution and to ensure that theremainder of this phase is precipitated in the form of very finelydispersed particles. Extrusions with very good mechanical properties canbe produced at favourable extrusion pressures and speeds if ingotshomogenised in this way are reheated quickly to the extrusiontemperature. However the surface finish'of extrusions produced from suchingots is not always as good as is desired.

The surface finish of an extrusion is to a large extent dependent on thespeed at which the metal is forced past the die. It is an object of thepresent invention to provide an improvement of the Alloy 6063composition and of like Al-Mg-Si alloys having magnesium and siliconlevels in the ranges referred to above, which permits an increase in theextrusion rate without loss of surface finish of the extrusion orconversely to provide a better standard of surface finish without changeof extrusion rate as compared with a typical specimen of Alloy 6063coming within the general specification.

A principal cause of defects in the quality of the surface finish ofAlloy 6063 extrusions is the breaking away of solid components from thesurface of the metal as it is forced through the die orifice. Thesedefects manifest themselves as light-coloured micro score-lines or tearson the surface of the extrusion and are commonly referred to as pick-up.Generally, the incidence of pick-up and its deleterious effect on thereflectivity and smoothness of the surface of the'extruded metalincrease with the extrusion speed.

It has now been postulated that one of the principal causes of surfacedefects from pick-up is due to the presence of the intermetallic phasecalled B-Al-Fe-Si in the ingot during the extrusion process. This phase,which is insoluble under the normal homogenisation conditions referredtoabove, grows in the form of thin, brittle sheets and is formed duringthe production of the ingot by the direct chill, casting process. TheB-Al- Fe-Si is.believed to have the chemical formula Fe -Si Al and has amonoclinic type crystal structure. The insoluble Fe-rich phase can alsobe present in a different form, a-Al-Fe-Si, This phase is believed tohave a chemical formula Fe -Si-Al, and has a cubic type crystalstructure. It has now been found that substantial re duction in pick-updefects can be achieved if the Al-Fe- Si phase present in the ingotduring extrusion is in the oZ-phase, believed to be because it is lessmechanically brittle'than the B-form. This is particularly true whilstthe level of iron in the alloy is maintained within the range of0.050.3%. Above 0.3 Fe pick-up tends to increase, irrespective of thephase of the aluminiumiron-silicon intennetallic compound, whilst below0.05% Fe the iron-rich phases are not detrimental to the surface qualityof the extruded section.

It has now been found that the addition of strontium or calcium inamounts of 0.01-0.5% in aluminiummagnesium-silicon alloys of the typeunder discussion results in at least a major proportion of the Al-Fe-Siphase in the as-cast ingot being in the a-phase. Other elements can betolerated in the alloy in substantial amount; Thusthe alloy may containup to 0.4% Cu, up to 0.1% each of Mn and Zn and a total of up to 0.15%(0.05% each)'of additional impurities without losing the benefitsarising from the Ca or Sr addition.

Whilst the addition of calcium or strontium in the stated amounts ishelpful in the improvement in the surface characteristics of extrusionsthroughout the whole range of the magnesium and silicon contents statedinitially, it is preferred to hold the magnesium content below 0.7% andthe combined total of magnesium plus silicon below 1.5%.

Whilst, as stated above, addition of calcium or strontium in amounts of0.01 to 0.5% is envisaged, most of the benefits of the invention areobtained by an addition of about 0.02-0.05%. With the addition of Sr orCa in an amount of about 0.05% substantially the whole of the Al-Fe-Siphase is in the a-form in the as-cast ingot. Whilst the as-cast ingotcan be extruded quite satisfactorily at relatively low speeds withoutfurther heat treatment, higher extrusion rates may be achieved byheating the ingot above the Mg si solvus temperature for sufficient timeto bring the Mg Si phase into solution. The level of the Sr or Caaddition is preferably held at about 0.020.05% because substantially thewhole of the benefit of the addition has been achieved at that level.Above that level little, if any, improvement in surface properties isobtained and there is a gradual decrease in the strength of the alloy.It is possible to add both Ca and Sr, the effect being substantiallyadditive. However, there is no advantage in so doing and it isinconvenient operationally. Where Sr and Ca are added together the totaladdition of the two components should be within the range above stated.

We have found that the a-Al-Fe-Si phase is also promoted by the additionof one or more of Na, Be and B to alloys falling within the presentclass. However it is not practicable, for various reasons, toincorporate these elements in the required amount in normal commercialoperations. For example, additions of Be would introduce potentialtoxicity problems.

One alloy according to the invention had the following composition: Si0.400.50%, Mg 0.450.55%, Fe 0.150.25%; Sr or Ca 0.01 50.05%; total otherimpurities 0.2% (max), Al balance. This alloy was cast into roundextrusion ingots by the DC. casting process and the ingots were heattreated at temperatures between 500 and 580C, for about 1 hour, tosolutionise the magnesium silicide. When this material was extruded itwas found that there was a significant improvement in the specularreflectivity and smoothness of the extrusions as compared with theextrusions of the same alloy (but without either the Sr or Ca addition).

In one series of tests this alloy containing 0.0 l 8% Ca (a), and 0.05%Ca (b), was compared with the standard, Ca-free, alloy (c). The ingotswere extruded, after reheating to 425C, at 150 ft./min. with thefollowing results:

Specular Reflectivity 4671 72% 23% Image Clarity 19 25 17 whiteness 483X 72 Visual Comparison Nil pick-up Nil pick-up Pick-up Measured bymethods described by B.W. Robinson in Metal Finishing, February 1970.

Specular Reflectivity 35% 51% 30% Image Clarity 36 37 29 whiteness 61 5166 Light Heavy Visual Comparison pick-up Nil pick-up pick-up It willthus be seen that significant improvement in extrusion characteristicshas been obtained.

In further tests the same alloy was tested at levels of Sr 0.2% and 0.5%and Ca at 0.2 and 0.5%.

These were extruded through the same die as in the preceding test at 275ft./min. and were compared with the standard alloy (c) under the sameconditions.

The alloys having Ca and Sr additions extruded with a very bright andpick-up-free surface, whereas the surface of the extrusions from thestandard alloy were dull and exhibited heavy pick-up.

We claim:

1. An as-cast aluminium magnesium silicide alloy extrusion ingotcontaining Al-Fe-Si, said alloy consisting essentially of 0.3-1 .2% Mg,0.2-1.2% Si, up to 0.4% Cu and up to 0.1% each Zn, Mn, ODS-0.3% Fe asimpurity and 0.15% total (0.05% each) other impurities, balancealuminum, characterized by the presence of Sr and/or Ca in a totalamount of 0.0 l-0. 5% for causing at least a major proportion of theAl-Fe-Si in the as-cast ingot to be in the a phase, thereby to reducepickup upon extrusion of the ingot.

2. An aluminium alloy according to claim 1 in which the total content ofSr and/or Ca is in the range of 0.020.05%.

3. An aluminium alloy according to claim 1 in which the content of Mg isbelow 0.7% and the sum of the content of Mg and Si is below 1.5%.

4. A homogenized aluminium magnesium silicide alloy extrusion ingotcontaining Al-Fe-Si, said alloy consisting essentially of 0.3-1 .2% Mg,0.2-1.2% Si, up to 0.4% Cu and up to 0.1% each Zn, Mn, 0.050.3% Fe asimpurity and 0.15% total (0.05% each) other impurities, balancealuminium, characterized by the presence of Sr and/or Ca in a totalamount of 0.0 l0.5%; at least a major proportion of the Al-Fe-Si in theingot being in the a phase, thereby effecting reduction in pickup uponextrusion of the ingot.

5. An aluminium alloy according to claim 4 in which the total content ofSr and/or Ca is in the range of 002-0055.

6. An aluminium alloy according to claim 4 in which the content of Mg isbelow 0.7% and the sum of the content of Mg and Si is below 1.5%.

7. An aluminium alloy ingot extrusion containing Al- Fe-Si, said alloyconsisting essentially of 0.3-1.2% Mg, 0.2-1.2% Si, 0.010.5% of analloying element selected from the class consisting of Sr and Ca,0.050.3% Fe, up 'to 0.4% Cu, up to 0.1% each of Zn and Mn, 0.15% total(0.05% each) other impurities, balance Al, characterized by beingessentially free from pickup and having good specular reflectivity,image clarity and whiteness; at least a major proportion of the Al-Fe-Siin the extrusion being in the a phase.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CQRREUHQNPATENT NO. 3,926,690 DATED December 16, 1975 INVENTOR(S) Larry RoyMorris and Frederick Barry Miners It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

Col. 2, line 21, "pick-up" should be enclosed within quotation marks.

Col. 1, line 37, "0.055" should read --O.,O5%-=- Bigncd and thisThirty-first D3? of August 1976 Arrest:

RUTH c. MASON c. MARSHALL DANN Arresting Officer Commissioner ufiarenrsand Trademarks

1. AN AS-CAST ALUMINIUM MAGNESIUM SILICIDE ALLOY EXTRUSION INGOTCONTAINING AL-FE-SI, SAID ALLOY CONSISTING ESSENTIALLY OF 0.3-1.2% MG,0.2-1.2% SI, UP TO 0.4$ CU AND UP TO 0.1% EACH ZN, MN, 0.05-0.3% FE ASIMPURITY AND 0.15% TOTAL (0.05% EACH) OTHER IMPURITIES, BALANCEALUMINUM, CHARACTERIZED HY THE PRESENCE OF SR AND/OR CA IN A TOTALAMOUNT OF 0.01-0.5% FOR CAUSING AT LEAST A MAJOR PROPORTION OF THEALFE-SI IN THE AS-CAST INGOT TO BE IN THE A PHASE, THEREBY TO REDUCEPICKUP UPON EXTRUSION OF THE INGOT.
 2. An aluminium alloy according toclaim 1 in which the total content of Sr and/or Ca is in the range of0.02-0.05%.
 3. An aluminium alloy according to claim 1 in which thecontent of Mg is below 0.7% and the sum of the content of Mg and Si isbelow 1.5%.
 4. A homogenized aluminium magnesium silicide alloyextrusion ingot containing Al-Fe-Si, said alloy consisting essentiallyof 0.3-1.2% Mg, 0.2-1.2% Si, up to 0.4% Cu and up to 0.1% each Zn, Mn,0.05-0.3% Fe as impurity and 0.15% total (0.05% each) other impurities,balance aluminium, characterized by the presence of Sr and/or Ca in atotal amount of 0.01-0.5%; at least a major proportion of the Al-Fe-Siin the ingot being in the Alpha phase, thereby effecting reduction inpickup upon extrusion of the ingot.
 5. An aluminium alloy according toclaim 4 in which the total content of Sr and/or Ca is in the range of0.02-0.055.
 6. An aluminium alloy according to claim 4 in which thecontent of Mg is below 0.7% and the sum of the content of Mg and Si isbelow 1.5%.
 7. An aluminium alloy ingot extrusion containing Al-Fe-Si,said alloy consisting essentially of 0.3-1.2% Mg, 0.2-1.2% Si, 0.01-0.5%of an alloying element selected from the class consisting of Sr and Ca,0.05-0.3% Fe, up to 0.4% Cu, up to 0.1% each of Zn and Mn, 0.15% total(0.05% each) other impurities, balance Al, characterized by beingessentially free from pickup and having good specular reflectivity,image clarity and whiteness; at least a major proportion of the Al-Fe-Siin the extrusion being in the Alpha phase.